The invention relates to an electro-hydrostatic actuator that is ideally suited to control the positioning of a valve or any other similar device.
More specifically, this invention relates to a compact electrically operated linear actuator that integrates all controls and components to provide rapid and efficient heat dissipation and cooling to all heat producing parts.
Current demands on power generation systems and valve controls require that the actuators be electrically controlled and include fail safe features. In many countries, linear actuator of the type herein disclosed also require certification when employed in an environment where an explosion might take place as for example in controlling valves utilized in gas or oil pipelines or in certain processing plants where volatile chemicals are used in the process. In order to gain certification, many of the actuators are housed in rather bulky complex structures and employ external power supplies and controls which are costly to construct and difficult to service and maintain in the field. Typically, the electronic controls of the actuator are designed to be located in separate remote housing having a non-hazardous controlled environment. The cabling between the actuator and the controller can be relatively long which can lead to signal transmission loses and other related difficulties.
The invention presented here provides a solution to electrical control actuation within a compact package and is designed to meet uniform cooling and protection for use in hazardous environments along with an integrated hydraulic failsafe system for rapidly bringing the actuator to a shut down position when a potentially hazardous situation is sensed.
In U.S. Pat. No. 2,631,431 to Gerbe, there is disclosed an electro-hydraulic actuator in which an electric motor is located in a tank filled with oil. The motor is equipped with a hollow shaft and the shaft of a pump impeller is slidably contained within the hollow motor shaft. The impeller of the motor is arranged so that it can turn with the motor shaft while at the same time moving longitudinally along the axis of the shaft. The pump impeller is situated inside a hollow piston that is secured to a piston rod. The piston rod extends upwardly and passes out of the tank. In operation, the motor drives the impeller at a speed to increase the pressure of the oil on one side of the piston to a desired level wherein the piston and piston rod are displaced upwardly to position a linear device that is secured to the piston rod. A weight or spring is used to return the piston to its home position when the motor is de-energized.
Although the Gerbe device provides for improved motor cooling, the electronic controls for the motor are situated at a location remote from the tank that houses the motor and is therefore subject to all the problems associated with transmission lines of any appreciable length. Furthermore, because the electrical unit associated with the actuator must be housed in its own hazardous area container, the system is rather costly to build and maintain. The Gerbe device does not include a failsafe feature.